Enhancement of alkylation catalysts for improved supercritical fluid regeneration

ABSTRACT

A method of modifying an alkylation catalyst to reduce the formation of condensed hydrocarbon species thereon. The method comprises providing an alkylation catalyst comprising a plurality of active sites. The plurality of active sites on the alkylation catalyst may include a plurality of weakly acidic active sites, intermediate acidity active sites, and strongly acidic active sites. A base is adsorbed to a portion of the plurality of active sites, such as the strongly acidic active sites, selectively poisoning the strongly acidic active sites. A method of modifying the alkylation catalyst by providing an alkylation catalyst comprising a pore size distribution that sterically constrains formation of the condensed hydrocarbon species on the alkylation catalyst or by synthesizing the alkylation catalyst to comprise a decreased number of strongly acidic active sites is also disclosed, as is a method of improving a regeneration efficiency of the alkylation catalyst.

GOVERNMENT RIGHTS

The United States Government has rights in the following inventionpursuant to Contract No. DE-AC07-99ID13727 between the U.S. Departmentof Energy and Bechtel BWXT Idaho, LLC.

FIELD OF THE INVENTION

The present invention relates to a method of modifying a surface of acatalyst. More specifically, the present invention relates to a methodof modifying an alkylation catalyst to reduce formation of condensedhydrocarbon species on the alkylation catalyst.

BACKGROUND OF THE INVENTION

Alkylation reactions are used to add an alkyl group to a molecule thatis to be alkylated. Alkylation reactions are extensively used in thepetroleum industry to produce medium- or large-mass hydrocarbons fromsmaller molecules. The alkylation reaction is typically used to alkylatea high vapor pressure paraffin (an alkane) with an olefin (an alkene) toproduce a low vapor pressure, high-octane gasoline blend. This gasolineblend is a clean gasoline blend stream and provides 13%-15% of gasolinedemand in the United States. One important alkylation reaction in thepetroleum industry is the alkylation of isobutane with butene to produceisooctane. Currently, the alkylation reaction is catalyzed with aconcentrated liquid mineral acid, such as hydrofluoric acid or sulfuricacid. However, large acid volumes and acid-oil sludges are produced bythe mineral acid-catalyzed reaction, raising safety and environmentalconcerns. Disposal of the acid-oil sludge is subject to stringentenvironmental regulations, which adds considerable expense to thealkylation reaction. In addition, leakage of the acid, either as aliquid or a solid, is another significant safety concern.

To reduce the environmental concerns, solid alkylation catalysts havebeen used to catalyze the reaction. However, these solid alkylationcatalysts deactivate rapidly due to the accumulation of hydrocarbonspecies (also known as coke) on a surface of the solid alkylationcatalyst. Coking of the solid alkylation catalyst is caused by sidereactions that involve acid-catalyzed polymerization and cyclization ofthe reactants and/or reaction products, which produces highmolecular-weight compounds that undergo extensive dehydrogenation,aromatization, and further condensation. As the hydrocarbon speciesaccumulate, they deactivate the solid alkylation catalyst and decreaseits ability to effectively catalyze the alkylation reaction. Thesehydrocarbon species are difficult to remove from the solid alkylationcatalyst. The solid alkylation catalyst is typically regenerated orreactivated by burning off or gasifying the coke compounds. However,since these regeneration processes are oxidative and damage activity ofthe solid alkylation catalyst, the solid alkylation catalyst is onlycapable of being regenerated a few times. The rapid deactivation of thesolid acid catalyst also produces large volumes of the solid alkylationcatalyst that must be discarded, making the alkylation reaction andsubsequent regeneration of the solid alkylation catalyst economicallyand environmentally unacceptable.

U.S. Pat. No. 6,579,821 to Ginosar et al. (the “Ginosar '821 patent”),the disclosure of which is incorporated by reference herein, disclosesthe use of a supercritical fluid to regenerate the alkylation catalyst.The supercritical fluid is isobutane, isopentane, 2,3-dimethylbutane,2-methylpentane, 3-methylpentane, 2,3-dimethylpentane,2,4-dimethylpentane, 2-methylhexane, 3-methylhexane, 2,3-dimethylhexane,2,4-dimethylhexane, 2,5-dimethylhexane, 3,4-dimethylhexane, or2,3,4-trimethylhexane. Extractive properties of the supercritical fluidare used to remove the hydrocarbon species that are adsorbed onto thealkylation catalyst. As the supercritical fluid contacts the alkylationcatalyst, the adsorbed hydrocarbon species are dissolved and removed.The supercritical fluid regeneration process enables the alkylationcatalyst to be reactivated or regenerated more than fifty times.

While the supercritical fluid removes most of the hydrocarbon species,the supercritical fluid has limited ability to effectively removecondensed hydrocarbon species that are present on the alkylationcatalyst. As used herein, the term “condensed hydrocarbon species”refers to a hydrocarbon compound(s) that is formed by an alkylation oroligomerization reaction, followed by cyclization and/or dehydrogenationof the hydrocarbon species. As the condensed hydrocarbon speciesaccumulate on the alkylation catalyst, they limit the extent ofregeneration and the economics of using the supercritical fluidregeneration process.

Surface modification of catalysts used in various types of reactions isknown in the art to increase performance (activity) or to decreasedeactivation of the catalyst. As disclosed in Liu et al., “Surfacemodification of zeolite Y and mechanism for reducing naphtha olefinformation in catalytic cracking reaction,” App. Catal. A: General,264:225-228 (2004), a surface of zeolite Y is modified with a rare earthcompound and a phosphorus compound to improve acidity density andstrength in pores of the zeolite Y and to decrease surface aciditydensity of the zeolite Y. As disclosed in Inui et al., “Effect ofModification of Acid Sites Located on the External Surface of aGallium-Silicate Crystalline Catalyst on Reducing Coke Deposit inParaffin Aromatization,” Ind. Eng. Chem. Res., 36:4827-4831 (1997), acidsites on an external surface of MFI-type gallium-silicate crystals areselectively modified with cerium oxide. The cerium oxide is used toneutralize the acid sites, moderating deactivation of the MFI-typegallium-silicate crystals and reducing deposition of coke compounds onthe MFI-type gallium-silicate crystals. Chen et al., “Effects of surfacemodification on coking, deactivation and para-selectivity of H-ZSM-5zeolites during ethylbenzene disproportionation,” J. Molec. Catal. A:Chemical, 181:41-55 (2002), discloses modifying a surface of an H-ZSM-5zeolite by silica chemical vapor deposition (“Si-CVD”) or by acombination of lepidine adsorption and Si-CVD to improve the performanceof the H-ZSM-5 zeolite.

U.S. Pat. No. 6,440,886 to Gajda et al. discloses a surface-modifiedbeta zeolite that has decreased deactivation. The beta zeolite is usedto catalyze alkylation or transalkylation of an aromatic compound. Thesurface of the beta zeolite is modified by removing strong acid sites,such as by converting the strong acid sites to weaker acid sites thatare ineffective or less effective. To modify the catalyst, the betazeolite is exposed to a strong mineral acid, such as nitric acid,sulfuric acid, phosphoric acid, or hydrochloric acid. The beta zeoliteis then calcined at a temperature ranging from 550° C. to 700° C. InU.S. Pat. No. 5,043,307 to Bowes et al., a modified aluminosilicatezeolite is disclosed. The aluminosilicate zeolite is modified bysteaming to decompose template material and to remove zeolitic aluminum.The zeolite is then contacted with a dealuminizing agent to form awater-soluble aluminum complex. U.S. Pat. No. 5,237,120 to Haag et al.discloses isomerizing a terminal double bond olefin-containing organicfeedstock to an internal double bond olefin. The isomerization reactionis performed using a surface-modified double bond isomerization catalystthat is partially deactivated for acid catalyzed reactions. The doublebond isomerization catalyst is modified by chemisorbing asurface-deactivating agent to the surface. The surface-deactivatingagent is an amine, phosphine, phenol, polynuclear hydrocarbon, cationicdye, or organic silicon compound.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of modifying an alkylationcatalyst to reduce the formation of condensed hydrocarbon species on asurface thereof. The method comprises providing an alkylation catalystcomprising a plurality of active sites. The alkylation catalyst may beselected from the group consisting of a zeolite, silicate,aluminophosphate, sodium calcium silicoaluminate,silicoaluminophosphate, pillared silicate, clay, layered material,sulfated zirconia, alumina, silica, boria, phosphorous oxide, titaniumdioxide, zirconium dioxide, chromia, zinc oxide, magnesia, calciumoxide, silica-alumina, silica-magnesia, silica-alumina-magnesia,silica-alumina-zirconia, sulfated mixed-metal oxide, bauxite,diatomaceous earth, and mixtures thereof. The plurality of active siteson the alkylation catalyst may include a plurality of weakly acidicactive sites, intermediate acidity active sites, and strongly acidicactive sites. A base is adsorbed to a portion of the plurality of activesites to selectively poison the portion of the plurality of activesites, wherein the base prevents the formation of condensed hydrocarbonspecies on the portion of the plurality of active sites. In oneembodiment, the base may selectively poison the strongly acidic activesites. The base may be selected from the group consisting of ammonia, anamine, phosphine, pyridine, a substituted pyridine, acetonitrile,benzene, a benzene derivative, and mixtures thereof.

The present invention also relates to a method of modifying analkylation catalyst to reduce the formation of condensed hydrocarbonspecies thereon by at least one of providing an alkylation catalystcomprising a pore size distribution that sterically constrains formationof a condensed hydrocarbon species on the alkylation catalyst andsynthesizing the alkylation catalyst to comprise a decreased number ofstrongly acidic active sites. The pore size distribution on thealkylation catalyst may be selected so that the pore size distributionis smaller than a size of the condensed hydrocarbon species. In oneembodiment, the pore size distribution may range from approximately 5 Åto approximately 8 Å. The alkylation catalyst may comprise a decreasednumber of strongly acidic active sites by synthesizing a zeolitecomprising a silicon/aluminum (“Si/Al”) ratio ranging from approximately2.5 to approximately 15.

The present invention also relates to a method of improving aregeneration efficiency of an alkylation catalyst. The method comprisesproviding an alkylation catalyst comprising a plurality of active sites.The active sites may comprise a plurality of weakly acidic active sites,intermediate acidity active sites, and strongly acidic active sites. Abase is adsorbed to a portion of the plurality of active sites and maybe selected from the group consisting of ammonia, an amine, phosphine,pyridine, a substituted pyridine, acetonitrile, benzene, a benzenederivative, and mixtures thereof. The base may be adsorbed to thestrongly acidic active sites. The base prevents the formation ofcondensed hydrocarbon species on the alkylation catalyst. The alkylationcatalyst is used to catalyze an alkylation reaction. During thealkylation reaction, hydrocarbon species may form on the alkylationcatalyst. The alkylation catalyst is exposed to supercritical fluidregeneration to substantially regenerate the alkylation catalyst bysubstantially removing the hydrocarbon species from the alkylationcatalyst.

The present invention also relates to a method of improving aregeneration efficiency of an alkylation catalyst. The method comprisesproviding an alkylation catalyst comprising a pore size distributionthat sterically constrains formation of condensed hydrocarbon species onthe alkylation catalyst. The pore size distribution may be selected tobe smaller than a size of the condensed hydrocarbon species. In oneembodiment, the pore size distribution ranges from approximately 5 Å toapproximately 8 Å. The alkylation catalyst is used to catalyze analkylation reaction, in which hydrocarbon species may be formed on thealkylation catalyst. The alkylation catalyst is exposed to supercriticalfluid regeneration to substantially regenerate the alkylation catalystby substantially removing the hydrocarbon species.

The present invention also relates to a method of improving aregeneration efficiency of an alkylation catalyst that comprisessynthesizing the alkylation catalyst to comprise a decreased number ofstrongly acidic active sites. The decreased number of strongly acidicactive sites prevents the formation of condensed hydrocarbon species onthe alkylation catalyst. In one embodiment, the alkylation catalyst maybe a zeolite comprising a silicon/aluminum ratio ranging fromapproximately 2.5 to approximately 15. The alkylation catalyst is usedto catalyze an alkylation reaction, in which hydrocarbon species may beformed on the alkylation catalyst. The alkylation catalyst is exposed tosupercritical fluid regeneration to regenerate the alkylation catalystby substantially removing the hydrocarbon species.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention may be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1 shows a plot of USY zeolite activity as measured by buteneconversion;

FIG. 2 shows a plot of product yield as a function of time on stream(total products C₅ and above (Δ), octanes (⋄), pentanes (□), hexanes(∘), heptanes (+), and total C₉ and above (X));

FIG. 3 shows a plot of C₈ yield in a product stream as a function oftime on stream (total octanes (⋄), trimethylpentanes (Δ),dimethylhexanes (□), and other C8 hydrocarbons (∘));

FIG. 4 shows a temperature programmed oxidation (“TPO”) plot of USYzeolite samples before supercritical fluid regeneration (“SFR”);

FIG. 5 shows a temperature programmed desorption (“TPD”) of USY zeolitesamples before SFR;

FIG. 6 shows a TPO plot of USY zeolite samples after SFR;

FIG. 7 shows a TPD plot of USY zeolite samples after SFR;

FIG. 8A shows Diffuse Reflectance Infrared Fourier TransformSpectroscopy (“DRIFTS”) spectra in the CH and OH stretching region ofUSY zeolite samples before SFR;

FIG. 8B shows DRIFTS spectra in the CC stretching and CH deformationregion of USY zeolite samples before SFR;

FIG. 9A shows DRIFTS spectra in the CH and OH stretching region of USYzeolite samples after SFR;

FIG. 9B shows DRIFTS spectra in the CC stretching and CH deformationregion of USY zeolite samples after SFR;

FIG. 10 shows Ultraviolet-visible (“UV-Vis”) spectra of USY zeolitesamples before SFR;

FIG. 11 shows UV-Vis spectra of USY zeolite samples after SFR;

FIG. 12 shows a plot of trimethylpentane yield as a function of time;

FIGS. 13 and 14 show TPO plots of USY zeolite;

FIGS. 15 and 16 show TPO plot of Beta zeolite;

FIG. 17 shows DRIFTS spectra in the CH and OH stretching region of USYzeolite samples before and after SFR;

FIG. 18 shows DRIFTS spectra in the CC stretching and CH deformationregion of USY zeolite samples before and after SFR;

FIG. 19 shows DRIFTS spectra in the CH and OH stretching region of Betazeolite samples before and after SFR;

FIG. 20 shows DRIFTS spectra in the CC stretching and CH deformationregion of Beta zeolite samples before and after SFR;

FIG. 21 shows UV-Vis spectra of USY zeolite samples before and afterSFR; and

FIG. 22 shows UV-Vis spectra of Beta zeolite samples before and afterSFR.

DETAILED DESCRIPTION OF THE INVENTION

An alkylation catalyst having a modified surface is disclosed. Themodified surface substantially reduces or eliminates formation ofcondensed hydrocarbon species on the alkylation catalyst. When present,the condensed hydrocarbon species reduce the effectiveness ofsupercritical fluid regeneration of the alkylation catalyst. The surfaceof the alkylation catalyst may be modified by at least one ofselectively poisoning a portion of active sites on the alkylationcatalyst, by selecting a pore size distribution on the alkylationcatalyst to hinder formation of the condensed hydrocarbon species, andby manufacturing the alkylation catalyst to include fewer sites that areactive for the formation of the condensed hydrocarbon species. Byreducing the formation of the condensed hydrocarbon species, thealkylation catalyst may be more effectively regenerated or reactivatedby the supercritical fluid regeneration. The supercritical fluidregeneration may also be performed at less frequent intervals, allowingthe alkylation catalyst to be used for a longer period of time beforeregeneration is needed. The alkylation catalyst having the modifiedsurface may also be regenerated in a shorter amount of time and may havean increased longevity than an alkylation catalyst lacking the surfacemodification.

As described in more detail herein, the condensed hydrocarbon speciesmay be polyolefinic hydrocarbons, aromatic hydrocarbons, dehydrogenatedaromatic hydrocarbons, cyclic or polycyclic hydrocarbons, graphitic cokecompounds, or mixtures thereof. These condensed hydrocarbon species maybe formed during an alkylation reaction catalyzed by the alkylationcatalyst or during regeneration or reactivation of the alkylationcatalyst. As used herein, the terms “regenerate,” “reactivate,” or otherverb forms thereof refer to treating the alkylation catalyst to renderthe alkylation catalyst into a form in which it is suitable forefficient use or reuse as the alkylation catalyst. The condensedhydrocarbon species may have greater than or equal to 9 carbon atoms andmay arise primarily from oligomerization, dehydrogenation, orcyclization of reactants or products of the alkylation reaction.Precursors or reaction intermediates for the condensed hydrocarbonspecies may include, but are not limited to, allylic carbocations,monoenylic carbocations, dienylic carbocations, polyenylic carbocations,or mixtures thereof.

The alkylation catalyst may be modified to reduce a number of sites onits surface that are active for the formation of the condensedhydrocarbon species. As such, the formation of the condensed hydrocarbonspecies on the alkylation catalyst may be reduced or eliminated. Thenumber of active sites may be decreased to a number sufficient toprevent the formation of the condensed hydrocarbon species withoutsubstantially affecting the catalytic performance of the alkylationcatalyst. In other words, a sufficient number of total active sites mayremain on the alkylation catalyst to catalyze the alkylation reaction.However, the number of active sites that may contribute to the formationof the condensed hydrocarbon species may be substantially reduced.

The alkylation catalyst may be a solid alkylation catalyst havingsufficient strength to catalyze the alkylation reaction. The alkylationcatalyst may include a plurality of acidic active sites, which arepresent in a distribution of acidities that ranges from weakly acidic tostrongly acidic. In other words, the acidic active sites may includeweakly acidic active sites, active sites that are intermediate inacidity, and strongly acidic active sites. Out of these acidic activesites, the weakly acidic active sites and the intermediate acidityactive sites may not substantially contribute to the formation of thecondensed hydrocarbon species. However, it is believed that the mostacidic, or strongly acidic, active sites may be substantiallyresponsible for the formation of the condensed hydrocarbon species.Therefore, to prevent the condensed hydrocarbon species from forming,the number of strongly acidic active sites on the alkylation catalystmay be reduced. For instance, the number of strongly acidic active sitesmay be decreased by from approximately 10% to approximately 20% comparedto the number of strongly acidic active sites on a conventional solidalkylation catalyst that lacks the surface modifications. To maintainthe performance of the alkylation catalyst, the corresponding activityof the alkylation catalyst may decrease less than approximately 10%.Alternatively, the strongly acidic active sites may be selectivelypoisoned so that the condensed hydrocarbon species are unable to form onthe alkylation catalyst.

To quantify or describe the relative acidities (weakly acidic,intermediate acidity, or strongly acidic) of the active sites, an amountof ammonia that adsorbs to the surface of the alkylation catalyst atdifferent temperatures may be used. The total number of acidic activesites (weakly acidic active sites, intermediate acidity active sites,and strongly acidic active sites) may be determined by the amount ofammonia adsorbed to the alkylation catalyst at 175° C. The ammonia maydesorb from a portion of the acidic active sites by evacuation at atemperature of 175° C. The active sites from which the ammonia desorbsat a temperature of 175° C. are referred to herein as the “weakly acidicactive sites.” In other words, the weakly acidic active sites are notable to retain adsorbed ammonia under evacuation at 175° C. while theintermediate acidity active sites and the strongly acidic active sitesretain adsorbed ammonia at this temperature. The amount of ammonia thatremains adsorbed to the alkylation catalyst (i.e., the amount of ammoniathat does not desorb from the alkylation catalyst) may be used todetermine the number of intermediate acidity active sites and stronglyacidic active sites. The acidities of the remaining active sites may bedetermined using a temperature gradient that ranges from approximately175° C. to approximately 540° C. At increasing temperatures, the ammoniamay desorb from the remaining acidic active sites, giving a profile fromwhich the number of intermediate acidity active sites and stronglyacidic active sites may be determined. The acidic active sites on whichthe ammonia remains adsorbed at a temperature greater than or equal toapproximately 450° C. are referred to herein as the “strongly acidicactive sites,” while the acidic sites from which the ammonia desorbs ata temperature ranging from approximately 175° C. to approximately 450°C. are referred to as the “intermediate acidity active sites.” Ingeneral, the total number of acidic active sites on the alkylationcatalyst may correspond to greater than 0.7 millimole of ammoniaadsorbed per gram of alkylation catalyst, the intermediate acidityactive site may correspond to greater than approximately 0.2 millimoleof ammonia adsorbed per gram of alkylation catalyst, and the stronglyacidic active sites may correspond to less than approximately 0.05millimole of ammonia adsorbed per gram of alkylation catalyst.

The alkylation catalyst may be selected by one of ordinary skill in theart depending on the alkylation reaction to be catalyzed. The alkylationcatalyst may be a solid alkylation catalyst that has the acidic activesites or is capable of achieving the acidic active sites when properlytreated, as known in the art. The alkylation catalyst may include, butis not limited to, a molecular sieve, such as a zeolite, silicate,aluminophosphate (“ALPO”), silicoaluminate, silicoaluminophosphate(“SAPO”), other metal aluminophosphates, a pillared silicate, clay(including kaolin and bentonite), a layered material, or mixturesthereof. The zeolite may be a natural zeolite, a synthetic zeolite, ormixtures thereof. The zeolite may include, but is not limited to, azeolite having the framework structure of FAU, MFI, MAZ, EMT, MEI, MTW,FER, EUO, MWW, OFF, MOR, BEA, LTL, zeolites that include rare-earthmetals, or mixtures thereof. In referring to the zeolites, standardnomenclature (as published by the International Zeolite Association) hasbeen used. Specific commercial examples of the zeolites include, but arenot limited to, Zeolite Socony Mobil-4 (“ZSM-4”), ZSM-3, ZSM-5, ZSM-20,ZSM-18, ZSM-12, ZSM-35, ZSM-48, ZSM-50, Mobil Composition of Matter-22(“MCM-22”), PSH-3, TMA offretite, TEA mordenite, REY (“Rare Earth Yzeolite”), faujasites including zeolite Y, mordenite, ultrastable Yzeolites (“USY”), zeolite beta, zeolite omega, zeolite L,clinoptilolite, zeolites that include rare-earth metals, or mixturesthereof. Zeolites are commercially available from numerousmanufacturers, such as Mallinckrodt Baker, Inc., (Phillipsburg, N.J.) orZeolyst International (Valley Forge, Pa.). Examples of thealuminophosphate include, but are not limited to, ALPO-5, VirginaPolytechnic Institute-5 (“VPI-5”), or mixtures thereof. Examples ofsilicoaluminophosphates include, but are not limited to, SAPO-5,SAPO-37, SAPO-31, SAPO-40, SAPO-41, or mixtures thereof. An example ofthe layered material includes MCM-36.

The alkylation catalyst may also be a sulfated zirconia (“S/ZrO₂”)catalyst, which is prepared by exposing zirconium hydroxide to sulfuricacid. The alkylation catalyst may also be an inorganic oxide, such asalumina (including beta- or gamma-alumina), silica, boria, a phosphorousoxide, titanium dioxide, zirconium dioxide, chromia, zinc oxide,magnesia, calcium oxide, silica-alumina, silica-magnesia,silica-alumina-magnesia, silica-alumina-zirconia, a sulfated mixed-metaloxide, bauxite, diatomaceous earth, or mixtures thereof.

The alkylation catalyst may be used in combination with a non-zeolitesubstance, such as a Lewis acid. The Lewis acid may be borontrifluoride, antimony pentafluoride, aluminum trichloride, or mixturesthereof. A refractory oxide may also be used in combination with thealkylation catalyst to provide temperature resistance. In addition, adiluent material, such as an oxide or clay, may be used with thealkylation catalyst to control the conversion rate, to improvemechanical properties of the alkylation catalyst, to provide a matrixmaterial, or to act as a binder. Other active substances, such asplatinum, palladium, or mixtures thereof, may also be used with thealkylation catalyst to provide a metal hydrogenation function.

In one embodiment, the number of active sites on the alkylation catalystmay be decreased by selectively poisoning at least a portion of theacidic active sites on the alkylation catalyst. Since the stronglyacidic active sites, as defined above, are believed to be responsiblefor the formation of the condensed hydrocarbon species, the portion ofthe acidic active sites that are selectively poisoned may be thestrongly acidic active sites. By selectively poisoning the stronglyacidic active sites, the condensed hydrocarbon species may be preventedfrom forming on the alkylation catalyst. The strongly acidic activesites may be selectively poisoned by exposing the alkylation catalyst toa base, such as ammonia, an amine, phosphine, pyridine, a substitutedpyridine, acetonitrile, benzene, a benzene derivative, or mixturesthereof. The alkylation catalyst may be exposed to the base at asufficient temperature and for a sufficient amount of time to adsorb thebase to the active sites, such as at a temperature ranging fromapproximately 100° C. to approximately 500° C. The base may also beadsorbed to the active sites under vacuum conditions by placing thealkylation catalyst in a chamber and evacuating the chamber. The basemay be allowed to enter into the evacuated chamber and adsorb onto thesurface of the alkylation catalyst. The alkylation catalyst may beexposed to the base for an amount of time ranging from approximately 1minute to approximately one hour.

Once adsorbed, the alkylation catalyst may be heated to a temperaturesufficient to desorb the base from a first portion of the active siteswhile the base remains adsorbed to a second portion of the active sites.For instance, the base may desorb from the weakly acidic active sitesand the intermediate acidity active sites while remaining adsorbed tothe strongly acidic active sites. The temperature used to desorb thebase from the first portion of the active sites may range fromapproximately 175° C. to approximately 440° C. The alkylation catalystmay be heated at this temperature for a sufficient amount of time, suchas from approximately 15 minutes to approximately two hours, to desorbthe base from the first portion of the active sites. Since the baseremains adsorbed to the strongly acidic active sites at a temperaturegreater than or equal to approximately 450° C., the strongly acidicactive sites may be selectively poisoned by the base.

The strongly acidic active sites may be selectively poisoned before thealkylation catalyst is used to catalyze the alkylation reaction. Forinstance, the strongly acidic active sites may be selectively poisonedafter the alkylation catalyst is synthesized or purchased.Alternatively, the strongly acidic active sites on the alkylationcatalyst may be selectively poisoned after the alkylation catalyst hasbeen used in the alkylation reaction for a predetermined amount of timeand has been subsequently regenerated. To poison the strongly acidicactive sites, the alkylation catalyst may be taken offline periodicallyand exposed to the base. The alkylation catalyst may also be selectivelypoisoned initially, before the alkylation catalyst is first used, andafter the alkylation catalyst has been used for a predetermined amountof time and regenerated.

The strongly acidic active sites may also be selectively poisoned byincorporating the base into the regeneration process. A small amount ofthe base may be dissolved in a supercritical fluid used in thesupercritical fluid regeneration process described in the Ginosar '821patent. For instance, the base may be present in the supercritical fluidat from approximately 0.001 millimole per gram of the alkylationcatalyst to approximately 0.1 millimole per gram of the alkylationcatalyst.

In another embodiment, the alkylation catalyst may be synthesized ormanufactured to include fewer strongly acidic active sites, preventingthe condensed hydrocarbon species from forming and accumulating on thealkylation catalyst. For instance, the alkylation catalyst may besynthesized to have a decreased number of strongly acidic active sites.As known in the art, the Si/Al ratio is a measure of the acidity of thealkylation catalyst. By adjusting the Si/Al ratio of the alkylationcatalyst and by applying post-synthesis methods, the alkylation catalystmay have a reduced number of strongly acidic active sites upon which thecondensed hydrocarbon species form. The Si/Al ratio of the zeolite mayrange from approximately 2.5 to approximately 15. Zeolites that fallwithin this range of Si/Al ratio are commercially available, such asfrom Mallinckrodt Baker, Inc. or Zeolyst International, or may besynthesized by conventional techniques.

The alkylation catalyst may also be manufactured at a temperature thatdecreases the formation of the strongly acidic active sites. For thesake of example only, if the alkylation catalyst is a commerciallyavailable USY zeolite in the ammonium form and is exposed to differentcalcining temperatures, the number and strength of strongly acidicactive sites that form on the alkylation catalyst may differ.

In another embodiment, the alkylation catalyst may have a pore sizedistribution that hinders the formation of the condensed hydrocarbonspecies. The alkylation catalyst may include a plurality of pores inwhich the alkylation reaction occurs. By selecting the size distributionof the pores on the alkylation catalyst to be smaller than the size ofthe condensed hydrocarbon species, the condensed hydrocarbon species maybe sterically constrained from forming on the alkylation catalyst.However, the pore size distribution of the alkylation catalyst may besufficiently large for the desired product of the alkylation reaction toform. To sterically constrain formation of the condensed hydrocarbonspecies, the pore size distribution of the alkylation catalyst may rangefrom approximately 5 Å to approximately 8 Å. The size of the pores maybe determined as known in the art, such as by estimating the voidstructure and pore dimensions using conventional nitrogen physisorptionmeasurements.

By modifying the surface of the alkylation catalyst, the formation ofthe condensed hydrocarbon species on the alkylation catalyst may bereduced or eliminated. Therefore, the alkylation catalyst may beregenerated more efficiently. The alkylation catalyst having themodified surface may be used to catalyze an alkylation reaction in thepetroleum industry or in another industry. For the sake of example only,the alkylation catalyst of the present invention may be used to catalyzethe reaction between a paraffin and an olefin to produce an alkylationproduct, as described in U.S. Pat. No. 6,103,948 to Ginosar et al. (the“Ginosar '948 patent”), the disclosure of which is incorporated byreference herein. The paraffin may be a compound that includes from 4 to8 carbon atoms, such as isobutane, isopentane, 3-methylhexane,2-methylhexane, 2,3-dimethylbutane, 2,4-dimethylhexane, analogs thereof,or mixtures thereof. The olefin may be a compound having from 2 to 12carbon atoms, such as 2-butene, 1-butene, isobutylene, propylene,ethylene, hexene, octene, heptene, or homologs thereof. In oneembodiment, the paraffin is isobutane and the olefin is 2-butene.

During the alkylation reaction, the hydrocarbon species may adsorb ontothe active sites of the alkylation catalyst in the form of carbocations.As used herein, the term “carbocation” refers to a positively chargedcarbonaceous compound and also refers to a surface alkoxide. Thehydrocarbon species formed during the alkylation reaction may includehydrocarbons that have low volatility and high molar mass. Thehydrocarbon species may be produced by side reactions during thealkylation reaction or may be introduced with the paraffin or olefinreactants. As the hydrocarbon species accumulate on the alkylationcatalyst, the number of active sites available to catalyze furtherreactions may decrease, deactivating the alkylation catalyst andreducing its efficiency. However, since the alkylation catalyst has themodified surface, the formation of the condensed hydrocarbon species onthe alkylation catalyst may be reduced or eliminated during at least oneof the alkylation reaction and the regeneration of the alkylationcatalyst.

As the alkylation reaction is performed, the alkylation catalyst maybecome partially deactivated or substantially completely deactivated bythe hydrocarbon species. However, since the formation of the condensedhydrocarbon species is reduced or eliminated by the modified surface ofthe alkylation catalyst, regeneration of the alkylation catalyst may bemore efficient. In other words, the alkylation catalyst may besubstantially completely regenerated using the supercritical fluidregeneration process described in the Ginosar '821 patent. Therefore,the alkylation reaction may also be allowed to proceed for longeramounts of time before regeneration of the alkylation catalyst isnecessary. In addition, when regeneration is needed, the regenerationmay be performed more quickly. During the regeneration process, theformation of additional condensed hydrocarbon species on the alkylationcatalyst may also be reduced or eliminated due to the modified surfaceof the alkylation catalyst.

Other regeneration processes known in the art may also be used toregenerate the alkylation catalyst. For instance, the alkylationcatalyst may be regenerated by oxidizing carbonaceous species in air oroxygen. However, since the oxidation process may decompose the base thatis adsorbed to the alkylation catalyst, additional base may be adsorbedonto the alkylation catalyst, as previously described, before re-usingthe alkylation catalyst. Alkylation catalysts may be regenerated byhydrogenating the carbonaceous species, allowing their desorption fromthe surface of the alkylation catalyst.

In contrast, if the alkylation catalyst used in the alkylation reactionis a solid alkylation catalyst that does not have its surface modifiedas described above, the hydrocarbon species and the condensedhydrocarbon species may form during the alkylation reaction. The amountof the hydrocarbon species and the condensed hydrocarbon species thatform on the alkylation catalyst may depend on an amount of time that thealkylation reaction is allowed to proceed before regenerating thealkylation catalyst, the paraffin/olefin feed ratio, the olefin weighthourly space velocity (“OWHSV”), and the alkylation temperature. Thecondensed hydrocarbon species may being to form on the unmodifiedalkylation catalyst as the alkylation reaction proceeds for longeramounts of time. For instance, if the alkylation reaction proceeds forapproximately 1 hour to approximately 3 hours, the condensed hydrocarbonspecies may be present on the unmodified alkylation catalyst in smallamounts and any deactivation of the unmodified alkylation catalyst maybe substantially due to the presence of the hydrocarbon species. Thehydrocarbon species may form on the unmodified alkylation catalyst whenthe unmodified alkylation catalyst has been contacted with up toapproximately 3 grams of olefin per gram of catalyst per hour. Incontrast, if the alkylation reaction proceeds for longer amounts oftime, such as from approximately 6 hours to approximately 8 hours,larger amounts of the condensed hydrocarbon species may form on theunmodified alkylation catalyst. The condensed hydrocarbon species mayform on the unmodified alkylation catalyst when the unmodifiedalkylation catalyst has been contacted with greater than approximately 3grams of olefin per gram of catalyst per hour. As such, after longerreaction times, the unmodified alkylation catalyst may be deactivated byboth the hydrocarbon species and the condensed hydrocarbon species.

As previously described, the condensed hydrocarbon species may includeunsaturated hydrocarbon species that are produced during the alkylationreaction. While regeneration of the unmodified alkylation catalyst mayeffectively remove a majority of the hydrocarbon species, a portion ofthe hydrocarbon species may remain on the unmodified alkylationcatalyst. In addition, the condensed hydrocarbon species or unsaturatedhydrocarbon species may remain on the unmodified alkylation catalyst.Additional condensed hydrocarbon species may also form on the unmodifiedalkylation catalyst during the regeneration because the hydrocarbonspecies remaining on the unmodified alkylation catalyst maydehydrogenate rather than being extracted by the supercritical fluid.For instance, aromatic hydrocarbons, polycyclic hydrocarbons, graphiticcoke compounds, or mixtures thereof on the unmodified alkylationcatalyst may be formed during the supercritical fluid regeneration.

On the unmodified alkylation catalyst, the supercritical fluidregeneration may be less than 100% effective because the condensedhydrocarbon species remain after the regeneration. In order to achieve100% effectiveness of the supercritical fluid regeneration on theunmodified alkylation catalyst, the reaction time of the alkylationreaction may be substantially reduced so that the condensed hydrocarbonspecies do not form on the alkylation catalyst. However, if thealkylation catalyst having the modified surface is used, the alkylationreaction may be performed for longer periods of time and thesupercritical fluid regeneration may be substantially 100% effective.

The following examples serve to explain embodiments of the presentinvention in more detail. These examples are not to be construed asbeing exhaustive or exclusive as to the scope of this invention.

EXAMPLES Example 1 Characterization of Hydrocarbon Species Remaining onan USY Zeolite before and after Supercritical Fluid Regeneration

The chemical nature of hydrocarbons remaining on an USY zeolite beforeand after supercritical isobutane regeneration (“SFR”) at 453 K and1.1×10⁷ Pa was determined. The USY zeolite was utilized for a liquidphase isobutane/butene alkylation reaction at 333 K and 1.1×10⁷ Pa.Samples of the USY zeolite were deactivated to different levels byrunning the alkylation reaction for different times on stream (“TOS”)and regenerated under flowing supercritical isobutane for 60 min.

Experimental

A precursor for the alkylation catalyst was the ammonium form of the USYzeolite (CBV-500 from Zeolyst International, Si/Al=2.6). The USY zeolitewas pelletized, crushed, and sieved, and the fraction between 8 and 20ASTM mesh was collected and calcined at 823 K for 3 hours to obtain theacid form of the alkylation catalyst.

A continuous flow reaction/regeneration experimental system thatincluded a stainless steel tube reactor housed in an electrically heatedaluminum block, high pressure feed pumps, a recycle pump, and an on-linegas chromatograph (“GC”) was employed. The reactor dimensions wereapproximately 44 cm in length by 8 mm internal diameter (“i.d.”). Thefluids were preheated in a tubing coil before entering the reactor. Forthe reaction step, the reactor was operated in partial recycle mode withthe aid of a turbo-micropump (Micropump, Inc. IDEX Co.), while theregeneration step was operated in a single pass mode. An ISCO model 260Dhigh pressure syringe pump was employed to pump the reactants, whichincluded a premixed 20:1 molar ratio of isobutane/2-butene feed, for thereaction step. Typical fresh feed molar composition as determined by GCanalysis was: isobutane 94.75%, trans 2-butene 2.83%, and cis 2-butene2.06%. The only detected impurities were propane (0.20%) and n-butane(0.16%). The fresh feed and recycle flowrates were 2.5 cm³/min and 50cm³/min, respectively. A second ISCO model 260D high-pressure syringepump was used to supply isobutane both to pressurize the system beforereaction and to regenerate the catalyst. Impurities in the isobutanestream included propane 0.23% and n-butane 0.29%. GC detection of thereactor effluent was performed on-line using a Hewlett Packard 5890Series II Gas Chromatograph equipped with an automated high-pressuresampling valve, a flame ionization detector (“FID”) and a 50 m×0.2 mm(1×i.d.) Supelco Petrocol column. The GC oven temperature was heldinitially at 323 K for 5 min, ramped to 423 K at 10 K/min, and held at423 K for 0.5 min.

Two sets of experiments were performed. The first set consisted of areaction step only, while the second set consisted of a reaction stepfollowed by a regeneration step. For each experiment, eight grams of theacid form of the USY zeolite was loaded in the reactor and pretreatedovernight in situ at 473 K under flowing helium. The temperature wasthen decreased to 333 K and the system pressurized at 1.1×10⁷ Pa withisobutane. At time zero, the flow of reactants (i.e., a mixture of theisobutane/2-butene feed) was initiated at a flow rate necessary toachieve an OWHSV of 0.5 g butene/(g catalyst×h). Samples of the productstream during reaction were analyzed by GC every 20 minutes. Theexperimental setup did not allow for product stream sampling duringregeneration.

For the reaction-only experiments, after the pre-selected TOS (60 min,180 min, 280 min, and 380 min) had elapsed, the reactant flow wasstopped, the system cooled down to room temperature, flushed with heliumat 3.4×10⁶ Pa for 2 hours, and the USY zeolite was recovered. About 0.5cm³ of the catalyst bed recovered from the reactor inlet, which usuallypresented a color slightly different than the rest of the catalyst bedand was contaminated with quartz wool particles from the inlet quartzwool plug, was discarded. The rest of the reactor content was mixed andused in subsequent analyses. These samples were assumed to represent thecatalyst conditions before regeneration.

For the reaction/regeneration experiments, after the pre-selected TOS(60 min, 180 min, 270 min, and 360 min) had elapsed, the reactant flowwas stopped, and 2 ml/min of isobutane at 1.1×10⁷ Pa was flowed throughthe reactor, the temperature was increased to 453 K over a period of 30min to achieve supercritical conditions and maintained at 453 K for 60min to regenerate the USY zeolite. Finally, the system was cooled down,flushed, and the USY zeolite recovered following the same procedure asdescribed for the reaction-only experiments.

Nitrogen physisorption measurements were performed on an automatedQuantachrome Autosorb-1C system. To minimize changes in the amount andnature of carbonaceous species retained on the surface of the USYzeolite, pretreatment of samples for nitrogen physisorption measurementsincluded outgassing at 298 K for 3 hours. Special care was taken toavoid sample exposure to environmental moisture before conducting anyanalysis including nitrogen physisorption measurements. The fresh USYzeolite sample was submitted to the same protocol as the USY zeolitessamples loaded in the reactor (i.e., overnight treatment in flowinghelium at 473 K and outgassing at 298 K for 3 hours afterwards). B.E.T.surface areas were calculated in the range of P/Po between 0.05 and 0.10and micropore volume was determined by the t-plot method, as known inthe art.

Temperature programmed oxidation (“TPO”) and temperature programmeddesorption (“TPD”) measurements were performed on a Perkin Elmer DiamondTG/DTA microbalance under 100 ml/min flowing air and nitrogen,respectively. Typically, 10 mg of sample were placed in the balance panand heated at 10 K/min from room temperature to 373 K. The temperaturewas maintained at 373 K for 30 min to allow for water desorption, andthen increased to 1073 K at 10 K/min. The change in weight was recordedand the negative of its derivative with respect to time utilized toreport TPO and TPD profiles. Because zeolites are able to retain watereven at temperatures as high as 773 K, it is not possible to completelyrule out a minimal contribution of water to the weight changes in thethermogravimetric analysis. However, continuous monitoring of the TPO orTPD product stream by quadrupole mass spectrometry revealed that m/e=17and 18 signals, which correspond to water, remained at baseline levelsabove 373 K in all experiments. Thus, it was assumed that all waterdesorbed at or below 373 K and the amount of hydrocarbons desorbed wascalculated from the change in weight with respect to the sample weightafter water desorption.

Diffuse reflectance infrared Fourier transform spectroscopy (“DRIFTS”)studies were performed at room temperature on a Nicolet Magna 750Fourier transform infrared spectrometer equipped with a commercialSpectratech diffuse reflectance cell. Eight-hundred-scan spectra werecollected in the 4000-400 cm⁻¹ range at a resolution of 4 cm⁻¹.Ultraviolet-visible (“UV-Vis”) diffuse reflectance spectroscopymeasurements were carried out on a Shimadzu UV-3101 PC scanningspectrophotometer equipped with an integrating sphere attachment. Asmall amount of powder USY zeolite sample was placed on paper andspectra collected in the 700-250 nm wavelength range.

USY Zeolite Deactivation Profile

Since a partially deactivated catalyst can be regenerated completely buta totally deactivated catalyst is less than fully regenerated, theeffectiveness of the SFR process was expected to depend on the degree ofdeactivation of the USY zeolite. A set of preliminary experiments wasperformed to determine TOSs at which to stop the reaction and start theSFR process, in order to have samples that represented the completedeactivation profile of the USY zeolite. Typical results obtained forUSY zeolite activity and selectivity are shown in FIGS. 1-3. Catalystactivity as measured by butene conversion is shown in FIG. 1. Catalystactivity was measured by butene conversion. For the first 120 min ofTOS, butene was converted completely. In other words, butene was notdetected in the fluid phase leaving the reactor. Between 120 min and 240min, conversion decreased to about 90% and, after 240 min, a pronounceddecrease was apparent. Trimethylpentane (“TMP”) production reached amaximum at around 120 min TOS and was insignificant after 360 min TOS,as shown in FIGS. 2 and 3. Distinct stages have been reported to occurin the deactivation profile of alkylation catalysts: (i) the initialactivity at time zero, which is difficult to observe; (ii) the usefullifetime of the catalyst, characterized by high conversion and slowdeactivation; (iii) the rapid deactivation, characterized by a fastdecrease of activity along with a change in selectivity to C₉₊ products;and (iv) the last stage, where catalyst deactivation is again slow andthe products are primarily C₉₊ products. The C₉₊ product composition inthe second stage is mostly C₈ isoparaffins due to alkylation activity,along with some production of C₅-C₇, which indicates cracking of olefinoligomers. During the third stage, activity for alkylation and crackingdecrease while oligomerization is maintained. The products during thelast stage are mainly C₉₊ that arise primarily from olefinoligomerization.

After considering the activity and selectivity profiles shown in FIGS.1-3, TOSs of 60 min, 180 min, 280 min, and ca. 380 min were selected tostop the reaction and perform the regeneration step. As used herein,samples before regeneration are denoted as 0, 60, 180, 280, and 380; andafter regeneration as 0R, 60R, 180R, 280R, and 360R. The numbersindicate the TOS spent under alkylation reaction.

USY Zeolite Characterization

The results of nitrogen physisorption measurements performed on the USYzeolite samples before regeneration are shown in Table 1. TABLE 1 USYZeolite Surface Area and Micropore Volume before SFR. Sample Fresh 0 60180 280 380 B.E.T. 768 758 498 287 106 107 surface area (m²/g) Micropore0.28 0.23 0.14 0.06 0.005 0.000 volume (cm³/g)Results for both fresh and blank experiment samples (i.e., sample 0) arealso included for comparison purposes. Note that fresh sample in Table 1denotes the acid form of the USY zeolite after overnight pretreatment at473 K under flowing helium and that sample 0 indicates a samplerecovered just after pressurizing the system with isobutane and withoutcontacting any reactant mixture. When compared to the fresh USY zeolite,all spent samples showed lower surface area and micropore volume, andthe loss in surface area and micropore volume increased with TOS.Micropore volume was negligible in sample 280 and below detection limitin sample 380, which indicated a completely filled/blocked microporesystem for a fully deactivated catalyst.

Table 2 shows the results of nitrogen physisorption measurements on USYzeolite samples submitted to SFR for 60 min at 453 K. TABLE 2 Catalystsurface area and micropore volume after SFR. Sample 0R 60R 180R 280R360R B.E.T. 748 705 698 722 645 surface area (m²/g) Micropore 0.24 0.230.23 0.23 0.24 volume (cm³/g)Data for a blank experiment (0R) sample is also included for comparisonpurposes. In this case, the blank experiment included pressurizing thesystem with isobutane at reaction temperature, increasing thetemperature to SFR conditions, and flowing supercritical isobutane for60 min. From Table 2, it is apparent that the SFR process produced asignificant recovery in sample surface area and micropore volume, above80% with respect to the fresh catalyst sample.Characterization of Adsorbed Hydrocarbons

Examples of TPO and TPD determinations performed on samples before andafter SFR are shown in FIGS. 4-7. TPO experiments run on samples beforeSFR (curves 60 to 380 in FIG. 4) revealed two differentiated peaks. Thefirst one, positioned between 373 K and 573 K, was assigned to therelease of low molecular weight hydrocarbons, and the second one,between 573 K and 923 K, was attributed to CO₂ produced by oxidation ofadsorbed hydrocarbons. These assignments were confirmed by massspectrometric analysis of the gaseous stream. Only the low temperature(first) peak was seen on the TPO profile of the blank experiment sample(curve 0 in FIG. 4). TPD under flowing nitrogen (FIG. 5) revealeddesorption of hydrocarbons up to about 673 K. Both, TPD and lowtemperature TPO peaks displayed maxima that shifted to highertemperatures with TOS, i.e., from around 425 K (sample 60) to 480 K(sample 380). The presence of shoulders on the TPD peaks indicateddesorption of a larger variety of hydrocarbons at higher temperatures.

FIGS. 6 and 7 show TPO and TPD profiles obtained from samples submittedto SFR. Carbon dioxide produced by TPO was found only from samplessubmitted to the two longest TOS (curves 280R and 360R in FIG. 6). Thefirst TPO peak maxima were observed at ca. 425 K-430 K regardless ofTOS.

Quantitative data for the amount of hydrocarbon species desorbed by TPOand TPD from all samples are summarized in Tables 3 and 4. The totalcontent of hydrocarbons measured on samples before SFR increased withTOS and ranged from 0.9% (sample 0) to 16.3% (sample 380). Althoughafter SFR (Table 4) the total amount of adsorbed hydrocarbons increasedalso with TOS, no detectable amount of CO₂ was produced from eithersample 60R or 180R. Samples 280R and 360R exhibited a lower amount ofhydrocarbons desorbing as the first peak and around 3.1% and 3.3% thatwas removed as CO₂, respectively. Most of the hydrocarbons present onsamples 280R and 360R desorbed as CO₂; in other words, more than 60% ofthe total desorption corresponded to the second TPO peak. TABLE 3Average Hydrocarbon Content before SFR as determined by TPD and TPOMeasurements Sample Min TOS 0 60 180 280 380 TPO (wt %) Hydrocarbon 0.95.1 6.5 6.0 7.2 desorbed below 573 K Hydrocarbons n.d. 4.0 6.0 9.0 9.1removed as CO₂ Total 0.9 9.1 12.5 15.0 16.3 TPD (wt %) Hydrocarbons 0.98.5 11.2 11.1 12.5 desorbed below 673 K(n.d. stands for not detected).

TABLE 4 Average Hydrocarbon Content after SFR as determined by TPD andTPO Measurements Sample Min TOS 0R 60R 180R 280R 360R TPO (wt %)Hydrocarbon 1.2 2.7 2.7 1.7 1.9 desorbed below 573 K Hydrocarbons n.dn.d. n.d. 3.1 3.3 removed as CO₂ Total 1.2 2.7 2.7 4.8 5.2 TPD (wt %)Hydrocarbons 1.2 2.8 2.7 1.7 1.8 desorbed below 673 K(n.d. stands for not detected).DRIFTS Analysis

FIGS. 8A-B and FIGS. 9A-B show the DRIFTS spectra of samples before andafter SFR, respectively. For hydrocarbons species, the CH stretchingregion generally spans from 2700 cm⁻¹ to 3100 cm⁻¹, and the CCstretching vibrations and the CH deformation vibrations are below 1650cm⁻¹ and 1465 cm⁻¹, respectively. For Y zeolites, bands at ca. 3745cm⁻¹, 3640 cm⁻¹, and 3540 cm⁻¹ are usually assigned to external terminalsilanol groups, hydroxyl groups of the supercages, and hydroxyl groupsof the β-cages, respectively. Peaks that correspond to skeletalvibrations of the zeolite framework are below ˜1500 cm⁻¹ and envelopsome of the low frequency hydrocarbon vibrations on the spectra ofhydrocarbons adsorbed on zeolites.

The DRIFTS spectrum of the fresh USY zeolite (FIG. 8A) showed thecharacteristic silanol and acidic OH stretching signals between 3500cm⁻¹ and 3800 cm⁻¹. More specifically, the silanol peak is revealed at3743 cm⁻¹, and the supercage and β-cage hydroxyl group peaks are seen at3670 cm⁻¹ and 3588 cm⁻¹, respectively. All spectra of samples submittedto reaction (i.e., 60 to 380 on FIG. 8A) displayed CH stretching bandsbetween 2800 cm⁻¹ and 3000 cm⁻¹, in which the contribution of theν_(as)CH₃ peak at 2963 cm⁻¹ was very important and the relativecontribution of ν_(as)CH₂ (aliphatic) at 2937 cm⁻¹ increased with TOS.At the same time, the hydroxyl band at 3670 cm⁻¹ decreased with TOS.Analyzing the spectra on the CC stretching and CH deformation region(FIG. 8B), a band at ca. 1635 cm⁻¹ is present in all spectra. Bandsaround 1635 cm⁻¹ are usually assigned to C═C stretching, but water alsoabsorbs infrared radiation at that frequency. Two more bands, ca. 1470cm⁻¹ and 1367 cm⁻¹, which may be assigned to CH deformation of CH₂ andCH₃ groups, are also seen on the spectra of samples submitted toreaction (curves 60 to 280).

FIGS. 9A-B shows the DRIFTS spectra of samples after SFR. Spectra ofregenerated samples (i.e., 60R-360R) displayed at least five peaks inthe silanol-hydroxyl region (FIG. 9A). Comparing with spectra of samplestaken before SFR (FIG. 8A), an improved definition of the peakcorresponding to supercage hydroxyl groups (3670 cm⁻¹) along with peaksat 3710 cm⁻¹ and 3564 cm⁻¹ was seen on all regenerated sample spectra.Low intensity CH stretching components between 2800 cm⁻¹-3000 cm⁻¹ aredisplayed by samples 180R, 280R, and 360R. A band ca. 1635 cm⁻¹ (FIG.9B) was found in all spectra and small peaks at 1540 cm⁻¹ and 1598 cm⁻¹on the spectra of samples 280R and 360R. Bands around 1540 cm⁻¹ areascribed to alkylnaphthalenes or polyphenylene structures, and around1580 cm⁻¹-1610 cm⁻¹ to complex mixtures of hydrogen-deficientcarbonaceous deposits. It is worth noting that none of the regeneratedsamples displayed spectra with CH deformation bands around 1470 cm⁻¹ or1370 cm⁻¹ (region not shown), as they did before SFR.

UV/Vis Analysis

Bands on UV-Vis spectra generally indicate the presence of unsaturatedspecies. Particularly, allylic, dienylic, and polyenylic carbocationshave been reported to absorb UV-Vis radiation between 290 nm-345 nm, 370nm-390 nm, and 430 nm-490 nm, respectively; and polycyclic aromaticcompounds around 410 nm. UV-Vis diffuse reflectance absorption spectraof samples before and after SFR are shown in FIGS. 10 and 11,respectively. Before SFR, at least monoenylic (315 nm) and dienylic (383nm) carbocations were detected on samples submitted to reaction up to280 min TOS (FIG. 10). The 280 min TOS sample also displayed spectrumfeatures that may be assigned to polycyclic aromatic compounds (broadband around 425 nm) and the 380 min TOS sample showed mostly polycyclicaromatic compounds.

After SFR (FIG. 11), bands around 425 nm assigned to polycyclic aromaticcompounds were apparent on the spectra of samples regenerated afterreacting for 180 or more min TOS (curves 180R, 280R, and 360R in FIG.11). It is worth mentioning that neither sample 0 nor 0R displayed anyUV-Vis absorption band that could correspond to unsaturatedcarbocations.

Results

The general decrease in nitrogen physisorption capacity and,particularly, the decrease in micropore volume with TOS of all samplesbefore regeneration (Table 1) indicated that hydrocarbon species wereadsorbed on the internal channels of the zeolite catalyst. A shift ofthe zeolite lattice vibration band, centered around 1308 cm⁻¹ on thefresh sample spectrum (not shown), to lower wavenumbers (i.e., 1270cm⁻¹) was found on the DRIFTS spectra of all samples before SFR. Bysubmitting those samples to outgassing, the intensity of all hydrocarbonbands decreased and the zeolite lattice vibration peak returned to 1308cm⁻¹. That shift confirmed that hydrocarbon species were located insidethe zeolite channels. The shift of the first TPO peak to highertemperatures and the TPD peak, which became broader and revealedshoulders, with TOS (FIGS. 4 and 5) indicated an increase of bothmolecular weight and diversity of adsorbed species as the USY zeolitedeactivated.

Comparing Table 2 with Table 1, it is apparent that the SFR process waseffective in recovering most of the surface area and micropore volume.Sample micropore volumes after SFR resembled the micropore volume of theblank experiment sample before regeneration (sample 0). Both 0 and 0Rsamples displayed nitrogen physisorption capacity, particularlymicropore volumes, lower than the fresh sample. This decrease may beattributed to the retention in the zeolite pores of hydrocarbon speciesthat may have been formed from isobutane and/or undetected unsaturatedimpurities. In addition, TPO and TPD measurements (i.e., curves 0 inFIGS. 4 and 5 and 0R in FIGS. 6 and 7) confirmed the presence ofhydrocarbons in both blank samples.

When correlating the relative loss of nitrogen physisorption capacity(Table 1) with the amount of hydrocarbons deposited on the zeolite poresas measured by TPO (Table 3), a somewhat direct correspondence is foundfor samples before regeneration. However, no obvious correspondencebetween nitrogen physisorption capacity and amount of adsorbedhydrocarbons was noticeable after SFR. Nevertheless, the amount ofhydrocarbons adsorbed on the zeolite pores after SFR was relativelysmall when compared with the amount before SFR. It is interesting tonote that although samples 360R and 0R presented similar microporevolumes, their hydrocarbon content was different, i.e., 5.2% and 1.2%respectively. Assuming a conservative case scenario, where thecarbonaceous deposits are as bulky as the 2,2,4-TMP whose density is 0.8cm³/g, 1.2% and 5.2% would correspond to a volume of 0.0096 cm³ and0.0416 cm³ per gram of sample, respectively. Then, instead of 0.24cm³/g, the expected micropore volume for sample 360R would have beenaround 0.20 cm³. Two reasons for this discrepancy may be the outgassingbefore nitrogen physisorption measurements, which may have removed partof the adsorbed species, and the fact that species more condensed (360R)occupy less volume.

It has been reported that the CO₂ peak in the TPO of deactivated zeolitealkylation catalysts arises from hydrocarbon restructuring fromaliphatic to aromatic during TPO heating. The absence of such a CO₂ peakin the TPO profile of samples 0R, 60R, and 180R (FIG. 6 and Table 4) mayindicate that the hydrocarbon species remaining after SFR are notexactly precursors of high temperature desorbing hydrocarbons andinstead of restructuring they were completely removed at low temperatureduring the TPO experiment. Before SFR, the only sample that displayedone TPO peak was the blank experiment sample. After SFR, not only the 0Rbut also the 60R and 180R samples displayed only the low temperature TPOpeak, which in general was neither shifted to higher temperatures norbroadened with TOS. In general, for samples 280R and 360R, the amount oflow temperature desorbing hydrocarbons removed by TPO and the totalhydrocarbons desorbed by TPD coincided, suggesting that no importantamount of low temperature desorbing hydrocarbons underwent restructuringtoward more condensed forms and that the CO₂ peaks were actuallyproduced by deposits already hydrogen deficient after SFR.

One might hypothesize that the SFR process extracted most cokeprecursors from samples that were regenerated while in their usefulcatalyst lifetime and that only weakly adsorbed low molecular weightspecies remained in the zeolite pores after SFR. In contrast, whenregeneration was initiated after the USY zeolite was at later stages ofdeactivation, the amount of high temperature desorbing hydrocarbonschanged from 9.0% and 9.1% (samples 280 and 360) to 3.1% and 3.3%(samples 280R and 360R), which accounts for the supercritical extractionof only around 65% of the high temperature desorbing hydrocarbons.

For samples submitted only to the reaction (curves 60 to 380 in FIG.8A), the diminished intensity of the hydroxyl band at 3670 cm⁻¹ suggeststhat such acid sites interact with hydrocarbon species and that thedeposits are located mainly in the supercages of the zeolite structure.The bands at 2800 cm⁻¹-3000 cm⁻¹ show the highly branched nature of thealiphatic species adsorbed on the zeolite surface, because of therelative high intensity of the ν_(as)CH₃ peak at 2963 cm⁻¹. Moreover,the relatively larger contribution of the ν_(as)CH₂ (aliphatic) at 2937cm⁻¹ at longer TOS with respect to the peak at 2963 cm⁻¹ would indicatean increase of hydrocarbon chain length with TOS in agreement with TPOprofiles that indicated an increase in molecular weight of adsorbedspecies with TOS (FIG. 4).

Although the band at 1635 cm⁻¹ (FIG. 8B) could be assigned to C═Cstretching, one must consider that, in order to avoid ageing of adsorbedspecies, the samples were not pretreated prior to DRIFTS analyses andthey could have adsorbed moisture from the environment. Water moleculesproduce a typical deformation band around 1640 cm⁻¹ when adsorbed onzeolite materials. In addition, the broad band between 2900 cm⁻¹-3500cm⁻¹ displayed by both fresh and 0 min TOS sample spectra in FIG. 8A isan indication of H-bonded OH stretching. This band may have obscured thepresence of CH stretching peaks on the blank sample spectrum (i.e.,sample 0 on FIG. 8A). Note that the blank sample did desorb hydrocarbonsby TPO and TPD determinations, and that a spectrum (not shown) revealinghydrocarbon-related bands was obtained when this sample was submitted tohigher temperatures in the DRIFTS cell.

The bands at 1470 cm⁻¹ and 1367 cm⁻¹ (FIG. 8B) displayed on the spectraof samples 60 to 380 may be assigned to CH deformation of CH₂ and CH₃groups. Bands at 1468 cm⁻¹ and 1375 cm⁻¹ have been assigned todeformation vibrations of the CH₂ and CH₃ groups of oligomeric speciesadsorbed on a zeolite catalyst, and at 1490 cm⁻¹ to deformations ofprimary or secondary carbocations or to CCC stretching of allyliccarbocations. Consequently, the bands at 1470 cm⁻¹ and 1367 cm⁻¹, whichbroadened with TOS, indicated an increase in the number of contributingspecies inter alia carbocations and oligomeric species with TOS.

Typically, bands around 1580 cm⁻¹-1610 cm⁻¹ are assigned to coke andhave been reported to arise from δ(CH) modes of a complex mixture ofhydrogen-deficient carbonaceous deposits (e.g., polyethenes and/oraromatics). Neither unsaturated CH stretching above 3000 cm⁻¹ nor cokebands (i.e., around 1580-1610 cm⁻¹) were found in any of the spectrataken on samples before SFR. After SFR, the presence of hydrocarbonspecies was detected by TPO, although CH stretching bands were hardlynoticeable on the DRIFTS spectrum of the blank experiment (0R) and the60R sample (FIG. 9A).

None of the regenerated samples presented obvious CH deformation bandsat around 1470 cm⁻¹ and 1367 cm⁻¹ (not shown) as they did before SFR.This behavior leads us to propose that the bands at 1470 cm⁻¹ and 1367cm⁻¹ correspond to relatively low molecular weight carbocations oroligomers that were desorbed and extracted from the zeolite pores by theSFR process. A band around 1540 cm⁻¹, ascribed to alkylnaphthalenes orpolyphenylene structures, appeared on the spectra of samples submittedto the longest TOS (280R and 360R in FIG. 9B). In addition, a coke bandat 1598 cm⁻¹ that increased with TOS is apparent on those two samplespectra. These two bands, along with the low intensity of the saturatedCH stretching bands, suggest the unsaturated nature of the hydrocarbonsremaining on the regenerated catalyst samples that were reactivatedafter reaching their last two stages of deactivation (i.e., the rapiddeactivation and the last stage).

Therefore, the comparison of DRIFTS spectra of samples before and afterSFR indicates that the SFR process extracted an important number of thespecies that covered the zeolite surface. However, samples that wereregenerated after having reached their last stages of deactivationcontained some hydrocarbon species that, instead of being extracted,dehydrogenated to produce more condensed hydrocarbon species. Thischange may be due to the longer TOSs under the alkylation reaction andthe higher temperature used for regeneration when compared to thealkylation reaction temperature, which both allowed for formation ofheavier coke precursors. The aging of adsorbed hydrocarbons may also beproduced by repeated reaction/regeneration cycles. USY zeolite samplessubmitted to four consecutive 180 min TOS reaction/60 min SFR cycles atan OVHSV of 0.5 g butene/(g catalyst×h), and their TPO and spectroscopicmeasurements demonstrated the presence of condensed hydrocarbon speciesboth before and after the last regeneration cycle.

The ability of a supercritical fluid to facilitate the hydride transferreaction between the supercritical fluid and the deactivatinghigh-molecular weight carbocations has been suggested as an importantproperty needed to attain high levels of catalyst activity recovery. Forregeneration initiated once the sample has been submitted to alkylationfor long TOSs, the diminished number of acid active sites strong enoughto catalyze hydride transfer reactions between isobutane and adsorbedcarbocations may also play a role in the incomplete removal of hightemperature desorbing hydrocarbons.

UV-Vis diffuse reflectance absorption spectra of samples before SFR(FIG. 10) revealed at least monoenylic (315 nm) and dienylic (383 nm)carbocations on samples submitted to reaction for up to 280 min TOS.Alkylcarbocations show no ultraviolet absorption above 210 nm. It isevident that the fast deactivation stage, in which the sample 280 wasrecovered, implies the onset of polycyclic aromatic compound formation.The last deactivation stage involves a lack of mono-unsaturatedcarbocations and the presence of neutral unsaturated species that can benoticed by the occurrence of a UV-Vis band around 425 nm.

Generally, DRIFTS and UV-Vis spectra of samples before SFR displayedfeatures that suggest that the chemical species adsorbed are largealkanes and alkenes, along with highly unsaturated and highly branchedspecies containing cyclic structures, which are increasingly aromatic astemperature increases. After SFR (FIG. 11), none of the samplesdisplayed important peaks corresponding to unsaturated carbocations.However, polycyclic compounds (absorbing at 425 nm) were obvious on the180R, 280R, and 360R sample spectra. Comparing FIGS. 10 and 11, thechange in hydrocarbon nature due to the SFR process is apparent. BeforeSFR, unsaturated carbocations were detected on all but the mostdeactivated sample (380) and, after SFR, mostly polycyclic aromaticcompounds were the unsaturated species remaining on the catalyst surfaceof the longer TOS samples (180R-360R). Presumably, the first TPO peak ofsamples after SFR is due to low molecular weight hydrocarbons, likelyisobutane, and the second one comes from compounds that produced boththe UV-Vis band around 425 nm and the 1598 cm⁻¹ DRIFTS band. One maypropose that although they are unsaturated species, their degree ofcondensation, at least on the sample submitted to 180 min TOS, is notextremely high. Note that although there is a 425 nm UV-Vis band (curve180R in FIG. 11), all hydrocarbons desorbed below 673 K and no CO₂ wasdetected in the TPO of the 180R sample. On the other hand, before SFRand because of the higher concentration of adsorbed hydrocarbons,hydrocarbon restructuring from aliphatic to aromatic upon TPO heatingmay contribute to the CO₂ peak in TPO measurements.

Heavier and more aromatic compounds, such as the ones detected afterregeneration of samples submitted to longer TOS, are expected to producea more toxic effect on catalyst activity recovery, as described in theGinosar '821 patent. In the Ginosar '821 patent, the effect ofregeneration was determined at different catalyst deactivation levels oncatalyst activity recovery. In the Ginosar '821 patent, recycle plugflow experiments utilizing multiple reaction/regeneration runs at OWHSVof 0.2 g butene/(g catalyst×h) were performed, which is a lower OWHSVthan that utilized herein. When the first reaction experiment wasconducted until the catalyst activity dropped to 95% (i.e., 6.5 h TOSunder the conditions at which their experiments were performed) and therest of reaction steps were maintained for 6.5 hours each, only about45% of catalyst activity recovery was found after 8reaction/regeneration cycles. Percentage catalyst activity recovery wasdefined as the integrated product yield per gram of catalyst withrespect to the first reaction step integrated yield. Furthermore, eachreaction step showed that the catalyst deactivated faster than on theprevious one, and 95% of initial activity was reached in shorter times,which was about 4 h in the last reaction step. On the other hand,catalyst activity and product yields scarcely decreased after 23regeneration steps, remaining at 100% of initial activity over theentire course of the experiment when the regeneration step was initiatedusing 3 h of alkylation as the regeneration criterion.

In conclusion, the alkylation reaction produced a decrease in USYzeolite surface area and pore volume due to the adsorption ofhydrocarbon species mainly in the supercages of the USY zeolitestructure. The molecular weight of those species, mostly highly branchedparaffins, increased with TOS. In addition, at longer TOS, neutralunsaturated hydrocarbons were detected by UV-Vis spectroscopy. The SFRprocess was effective in recovering surface area and micropore volume.The SFR process extracted most coke precursors from samples that weresubmitted to SFR after relatively short TOS under alkylation reactionconditions, when the levels of activity for TMP production were thehighest. Samples that were initially allowed to react for longer TOS(until reaching the fast deactivation and the last stage) may havecontained some hydrocarbon species, such as cyclic structures, thatinstead of being extracted by the supercritical fluid, dehydrogenated toproduce more condensed hydrocarbon species. This change may have beendue to the longer TOS, which allowed for an increase in the molecularweight and amount of coke precursors, and the higher temperature usedfor regeneration.

Example 2 The Effect of Pore Size on the Supercritical FluidRegeneration

The effect of pore size on the supercritical fluid regeneration of adeactivated alkylation catalyst was determined. Two zeolites havingdifferent pore size distributions were used to catalyze the alkylationreaction of isobutane and 2-butene to form TMP. One of the zeolites wasa USY zeolite (CBV 500) and the second zeolite was a Beta zeolite (CP814N). The USY zeolite has a FAU framework structure, a SiO₂/Al₂O₃ ratioof 5.2, and cages or cavities in its pore structure. The Beta zeolitehas a BEA framework structure and a SiO₂/Al₂O₃ ratio of 18, but does nothave cages or cavities in its pore structure.

The alkylation reaction was conducted in a reactor operated in partialrecycle mode for the alkylation reaction and single pass mode for thesupercritical fluid regeneration. A single reactor was operated for1-cycle experiments. Two reactors were operated in swing mode for4-cycle experiments. A premixed 20:1 molar ratio of isobutane:2-butenewas used as the feedstock at an OWHSV of 0.5 hr⁻¹. The alkylationreaction was performed for six hours at 60° C. and 111 bar. Thesupercritical fluid regeneration was performed at 180° C. for 60 minutesunder 2 ml/min of isobutane. As shown in FIG. 12, the USY zeoliteinitially had higher yields of TMP than the Beta zeolite. However, afterrepeated reaction/regeneration cycles, the Beta zeolite displayed higherstability.

TPO, DRIFTS, and UV-Vis spectroscopy measurements were performed on eachof the zeolites before and after the supercritical fluid regeneration.The TPO, DRIFTS, and UV-Vis spectroscopy measurements were conducted aspreviously described. The results of these analyses are shown in FIG.13-22.

The surface area (“SA”) and the micropore volume (“MPV”) of each of thezeolites were determined by conventional techniques before and after thesupercritical fluid regeneration (“SFR”), as shown in Table 5. TABLE 5Surface Area and Micropore Volume of the USY-zeolite and theBeta-zeolite. USY zeolite Beta zeolite Fresh SA (m²/g) 768 628 MPV 0.280.19 (cm³/g) Spent 1- Before 1^(st) SA (m²/g) 107 204 cycle SFR MPV 0.000.00 (cm³/g) After 1^(st) SA (m²/g) 645 477 SFR MPV 0.24 0.10 (cm³/g)Spent 4- Before 4^(th) SA (m²/g) 89 156 cycle SFR MPV 0.00 0.00 (cm³/g)After 4^(th) SA (m²/g) 465 602 SFR MPV 0.16 0.15 (cm³/g)The results show that the supercritical fluid regeneration was moreeffective in recovering surface area and micropore volume in the Betazeolite than in the USY zeolite. Without being bound to a particulartheory, it is believed that fewer condensed hydrocarbon species wereable to form on the Beta zeolite due to the lack of cages or cavities.

Example 3 The Effect of Zeolite Acidity and Pore Structure on the Natureof Coke Precursors and SFR

The effect of zeolite acidity and pore structure on the nature of cokeprecursors and the effectiveness of SFR was determined. A series of 12member-ring zeolites (“12 MR”) was submitted to an isobutane/butenealkylation reaction at 333 K and 1.1×10⁷ Pa and supercritical isobutaneregeneration at 453 K and 1.1×10⁷ Pa. The zeolite samples were fullydeactivated by running the liquid phase alkylation reaction for 6 h andregenerated under flowing supercritical isobutane for 60 min. Zeolitesamples were recovered and analyzed before and after SFR. A continuousflow reaction/regeneration experimental system was employed in thealkylation reaction. The reactants included a premixed 20:1 molar ratioof isobutane/2-butene feed for the reaction step. The OWHSV was 0.5 h⁻¹.Isobutane was utilized both to pressurize the system before reaction andto regenerate the zeolites. Samples of the product stream during thereaction were analyzed by gas chromatography every 20 minutes. Zeolitesamples were recovered before and after SFR and submitted to N₂physisorption, TPO, DRIFS, and UV-Vis spectroscopy measurements, theresults of which are summarized in Table 6. The acidity of fresh sampleswas determined by ammonia chemisorption. TABLE 6 Results for Acidity,Octane Yield, Hydrocarbon Content, and Zeolite Surface Area.Hydrocarbons % SA w.r.t by TPO fresh sample Sample* Acidity OctaneRegen- Regenerat- (Si/Al ratio) (μmol/g) yield (%) Spent erated Spent edCBV 712^(y) 509 15 3.9 0.0 63 87 (6) CBV 720^(y) 213 7 1.4 0.1 87 98(15) CP 814 N^(b) 741 42 11.5 2.6 32 76 (9) CP 814 E^(b) 345 19 10.0 8.428 36 (12.5) KL¹(3) 944 1 3.1 2.4 13 12 CBV 21 A^(m) 642 3 5.9 3.2 8 21(10)*Superscripts stand for: Y (y), beta (b), L (1), and mordenite (m)zeolites.

During alkylation and for similar ranges of acidity, the beta zeolitesproduced higher octane yields and higher amounts of coke precursors thanthe Y-zeolites. The loss of surface area due to the alkylation reactionon the L and mordenite zeolites along with the relatively low amount ofadsorbed hydrocarbons indicated the easier plugging of the pores in thezeolites having one-dimensional 12 MR structures. Among all of thestudied zeolites, the lowest recovery of surface area by SFR was foundin the L-zeolite, likely due to significant diffusion limitations. Onthe other hand, the best recoveries of surface area were obtained inzeolites that presented 3-dimensional pore structures, where diffusionlimitations were less important. DRIFTS bands around 1590 cm⁻¹, whichare usually assigned to hard coke species, were found only inregenerated Y-zeolite samples. This indicated that the presence ofzeolite cages and a 3-dimensional pore structure along with the highertemperatures utilized for the SFR (453 K) with respect to alkylation(333 K) favored hydrocarbon cyclization and condensation reactions inthe Y-zeolite channels. Despite the almost complete recovery of surfacearea in the Y-zeolite samples, the appearance of hard coke depositsafter SFR is expected to decrease the long-term recovery of activity ofthis zeolite after repeated reaction/regeneration cycles. AlthoughUV-Vis studies showed the presence of unsaturated carbocations in allsamples both before and after SFR, polycyclic/aromatic compounds (i.e.,band around 430 nm) prevailed mainly in the Y and L-zeolite samples.

As shown by these results, zeolite acidity and pore structure played animportant role in zeolite behavior during the SFR process. Absence ofcages and 3-dimensional pore structures in the zeolites favored theeffectiveness of the combined alkylation/SFR cycle. Among the zeolitesanalyzed, the beta zeolite with the higher acidity displayed the bestperformance by combining good octane yield during alkylation with highrecovery in surface area and little formation of hard coke deposits bySFR.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been described in detailherein by way of example only. However, it should be understood that theinvention is not intended to be limited to the particular formsdisclosed. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the following appended claims.

1. A method of modifying an alkylation catalyst to reduce the formationof condensed hydrocarbon species thereon, the method comprising:providing an alkylation catalyst comprising a plurality of active sites;and adsorbing a base to a portion of the plurality of active sites toselectively poison the portion of the plurality of active sites, whereinthe base prevents the formation of condensed hydrocarbon species on theportion of the plurality of active sites.
 2. The method of claim 1,wherein providing an alkylation catalyst comprising a plurality ofactive sites comprises providing an alkylation catalyst selected fromthe group consisting of a zeolite, silicate, aluminophosphate, sodiumcalcium silicoaluminate, silicoaluminophosphate, pillared silicate,clay, layered material, sulfated zirconia, alumina, silica, boria,phosphorous oxide, titanium dioxide, zirconium dioxide, chromia, zincoxide, magnesia, calcium oxide, silica-alumina, silica-magnesia,silica-alumina-magnesia, silica-alumina-zirconia, sulfated mixed-metaloxide, bauxite, diatomaceous earth, and mixtures thereof.
 3. The methodof claim 1, wherein providing an alkylation catalyst comprising aplurality of active sites comprises providing the alkylation catalystcomprising a plurality of weakly acidic active sites, intermediateacidity active sites, and strongly acidic active sites.
 4. The method ofclaim 1, wherein adsorbing a base to a portion of the plurality ofactive sites comprises exposing the alkylation catalyst to a baseselected from the group consisting of ammonia, an amine, phosphine,pyridine, a substituted pyridine, acetonitrile, benzene, a benzenederivative, and mixtures thereof.
 5. The method of claim 4, whereinexposing the alkylation catalyst to the base comprises exposing thealkylation catalyst to the base at a temperature ranging fromapproximately 100° C. to approximately 500° C.
 6. The method of claim 4,wherein exposing the alkylation catalyst to the base comprises adsorbingthe base to a plurality of weakly acidic active sites, intermediateacidity active sites, and strongly acidic active sites.
 7. The method ofclaim 6, further comprising desorbing the base from the weakly acidicactive sites and the intermediate acidity active sites.
 8. The method ofclaim 7, wherein desorbing the base from the weakly acidic active sitesand the intermediate acidity active sites comprises heating thealkylation catalyst to a temperature ranging from approximately 175° C.to approximately 440° C.
 9. The method of claim 1, wherein adsorbing abase to a portion of the plurality of active sites comprises selectivelypoisoning the strongly acidic active sites.
 10. A method of modifying analkylation catalyst to reduce the formation of condensed hydrocarbonspecies thereon, the method comprising at least one of providing analkylation catalyst comprising a pore size distribution that stericallyconstrains formation of a condensed hydrocarbon species on thealkylation catalyst and synthesizing the alkylation catalyst to comprisea decreased number of strongly acidic active sites.
 11. The method ofclaim 10, wherein providing an alkylation catalyst comprising a poresize distribution that sterically constrains formation of a condensedhydrocarbon species comprises selecting the pore size distribution to besmaller than a size of the condensed hydrocarbon species.
 12. The methodof claim 10, wherein providing an alkylation catalyst comprising a poresize distribution that sterically constrains formation of a condensedhydrocarbon species comprises providing the alkylation catalyst with apore size distribution that ranges from approximately 5 Å toapproximately 8 Å.
 13. The method of claim 10, wherein providing analkylation catalyst comprising a pore size distribution that stericallyconstrains formation of a condensed hydrocarbon species comprisesproviding the alkylation catalyst with the pore size distribution thatsterically constrains formation of polyolefinic hydrocarbons, aromatichydrocarbons, dehydrogenated aromatic hydrocarbons, cyclic or polycyclichydrocarbons, graphitic coke compounds, or mixtures thereof.
 14. Themethod of claim 10, wherein providing an alkylation catalyst comprisinga pore size distribution that sterically constrains formation of acondensed hydrocarbon species comprises providing the alkylationcatalyst with the pore size distribution that sterically constrainsformation of a precursor to the formation of the condensed hydrocarbonspecies, wherein the precursor is selected from the group consisting ofallylic carbocations, monoenylic carbocations, dienylic carbocations,polyenylic carbocations, and mixtures thereof.
 15. The method of claim10, wherein synthesizing the alkylation catalyst to comprise a decreasednumber of strongly acidic active sites comprises synthesizing a zeolitecomprising a silicon/aluminum ratio ranging from approximately 2.5 toapproximately
 15. 16. A method of improving a regeneration efficiency ofan alkylation catalyst, comprising: providing an alkylation catalystcomprising a plurality of active sites; adsorbing a base to a portion ofthe plurality of active sites to prevent the formation of condensedhydrocarbon species on the alkylation catalyst during an alkylationreaction; catalyzing the alkylation reaction with the alkylationcatalyst; and exposing the alkylation catalyst to supercritical fluidregeneration to substantially regenerate the alkylation catalyst. 17.The method of claim 16, wherein providing an alkylation catalystcomprising a plurality of active sites comprises providing thealkylation catalyst comprising a plurality of weakly acidic activesites, intermediate acidity active sites, and strongly acidic activesites.
 18. The method of claim 16, wherein adsorbing a base to a portionof the plurality of active sites comprises exposing the alkylationcatalyst to a base selected from the group consisting of ammonia, anamine, phosphine, pyridine, a substituted pyridine, acetonitrile,benzene, a benzene derivative, and mixtures thereof.
 19. The method ofclaim 18, wherein exposing the alkylation catalyst to the base comprisesexposing the alkylation catalyst to the base at a temperature rangingfrom approximately 100° C. to approximately 500° C.
 20. The method ofclaim 18, wherein exposing the alkylation catalyst to the base comprisesadsorbing the base to a plurality of weakly acidic active sites,intermediate acidity active sites, and strongly acidic active sites. 21.The method of claim 20, further comprising desorbing the base from theweakly acidic active sites and the intermediate acidity active sites.22. The method of claim 21, wherein desorbing the base from the weaklyacidic active sites and the intermediate acidity active sites comprisesheating the alkylation catalyst to a temperature ranging fromapproximately 175° C. to approximately 440° C.
 23. The method of claim16, wherein adsorbing a base to a portion of the plurality of activesites comprises selectively poisoning the strongly acidic active sites.24. The method of claim 16, wherein catalyzing the alkylation reactionwith the alkylation catalyst comprises forming hydrocarbon species onthe alkylation catalyst.
 25. The method of claim 16, wherein exposingthe alkylation catalyst to supercritical fluid regeneration tosubstantially regenerate the alkylation catalyst comprises substantiallyremoving the hydrocarbon species from the alkylation catalyst.
 26. Amethod of improving a regeneration efficiency of an alkylation catalyst,comprising: providing an alkylation catalyst comprising a pore sizedistribution that sterically constrains formation of condensedhydrocarbon species on the alkylation catalyst; catalyzing an alkylationreaction with the alkylation catalyst; and exposing the alkylationcatalyst to supercritical fluid regeneration to substantially regeneratethe alkylation catalyst.
 27. The method of claim 26, wherein providingan alkylation catalyst comprising a pore size distribution thatsterically constrains formation of condensed hydrocarbon species on thealkylation catalyst comprises selecting the pore size distribution to besmaller than a size of the condensed hydrocarbon species.
 28. The methodof claim 26, wherein providing an alkylation catalyst comprising a poresize distribution that sterically constrains formation of condensedhydrocarbon species comprises providing the alkylation catalyst with apore size distribution that ranges from approximately 5 Å toapproximately 8 Å.
 29. The method of claim 26, wherein providing analkylation catalyst comprising a pore size distribution that stericallyconstrains formation of condensed hydrocarbon species comprisesproviding the alkylation catalyst with the pore size distribution thatsterically constrains formation of polyolefinic hydrocarbons, aromatichydrocarbons, dehydrogenated aromatic hydrocarbons, cyclic or polycyclichydrocarbons, graphitic coke compounds, or mixtures thereof
 30. Themethod of claim 26, wherein providing an alkylation catalyst comprisinga pore size distribution that sterically constrains formation ofcondensed hydrocarbon species comprises providing the alkylationcatalyst with the pore size distribution that sterically constrainsformation of a precursor to the formation of the condensed hydrocarbonspecies, wherein the precursor is selected from the group consisting ofallylic carbocations, monoenylic carbocations, dienylic carbocations,polyenylic carbocations, and mixtures thereof.
 31. The method of claim26, wherein catalyzing an alkylation reaction with the alkylationcatalyst comprises forming hydrocarbon species on the alkylationcatalyst.
 32. The method of claim 26, wherein exposing the alkylationcatalyst to supercritical fluid regeneration to substantially regeneratethe alkylation catalyst comprises substantially removing the hydrocarbonspecies from the alkylation catalyst.
 33. A method of improving aregeneration efficiency of an alkylation catalyst, comprising:synthesizing the alkylation catalyst to comprise a decreased number ofstrongly acidic active sites in comparison to a conventional solidalkylation catalyst; catalyzing an alkylation reaction with thealkylation catalyst; and exposing the alkylation catalyst tosupercritical fluid regeneration to substantially regenerate thealkylation catalyst, wherein the decreased number of strongly acidicactive sites prevents the formation of condensed hydrocarbon species onthe alkylation catalyst.
 34. The method of claim 33, whereinsynthesizing the alkylation catalyst to comprise a decreased number ofstrongly acidic active sites comprises synthesizing a zeolite comprisinga silicon/aluminum ratio ranging from approximately 2.5 to approximately15.
 35. The method of claim 33, wherein catalyzing an alkylationreaction with the alkylation catalyst comprises forming hydrocarbonspecies on the alkylation catalyst.
 36. The method of claim 33, whereinexposing the alkylation catalyst to supercritical fluid regeneration tosubstantially regenerate the alkylation catalyst comprises substantiallyremoving the hydrocarbon species from the alkylation catalyst.